A typical wireless communication system includes a number of base stations each providing coverage in which to serve user equipment devices (UEs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped devices. In turn, each base station may sit as a node on a core access network that includes entities such as a network controller and a gateway system that provides connectivity with an external transport network such as the Internet. With this arrangement, a UE within coverage of the system could engage in air interface communication with a base station and may thereby communicate via the base station with various remote network entities or with other WCDs served by the base station.
Such a system could operate in accordance with a particular air interface protocol, examples of which include, without limitation, Long Term Evolution (LTE) (using Orthogonal Frequency Division Multiple Access (OFDMA) and Single Carrier Frequency Division Multiple Access (SC-FDMA), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), Global System for Mobile Communications (GSM), IEEE 802.11 (WIFI), BLUETOOTH, and others.
In accordance with the air interface protocol, a base station could provide service on one or more carriers, each spanning particular radio-frequency (RF) spectrum on which communications can flow wirelessly between the base station and UEs. Such a carrier could be structured to provide a downlink for carrying communications from the base station to UEs and an uplink for carrying communications from UEs to the base station. For instance, the carrier could be frequency division duplex (FDD), with separate frequency bandwidth provided respectively for downlink and uplink communication, or time division duplex (TDD), with a single frequency bandwidth being time division multiplexed between downlink and uplink use. Representative frequency bandwidths could be 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, or 20 MHz, among other possibilities.
Through modulation or other means on the carrier, the downlink and uplink could then be structured in accordance with the air interface protocol to define particular air interface resources for carrying communications between the base station and the UEs, and the base station could be configured to coordinate use of at least some of those resources as necessary.
Under LTE, for instance, the air interface is divided over time into a continuum of 10-millisecond frames, each of which is then further divided into ten 1-millisecond subframes or transmission time intervals (TTIs). In each TTI, the carrier bandwidth is then divided into 180-kHz-wide frequency blocks, referred to as physical resource blocks (PRBs), that can be modulated to carry data between the base station and UEs. And the base station is configured to allocate those PRBs for use to carry data on an as-needed basis. For instance, when the base station has data to send to a UE, the base station could allocate certain PRBs of a TTI on the downlink to carry that data and could transmit the data to the UE in those allocated PRBs of the TTI. And when a UE has data to send to the base station, the UE could send a scheduling request to the base station, the base station could allocate certain PRBs of an upcoming TTI on the uplink to carry the data, and the UE could then transmit the data to the base station in the allocated PRBs of that TTI.
More particularly, under LTE, each PRB is divided into an array of resource elements that could carry data communications using an applicable modulation and coding scheme (MCS) typically selected based on an evaluation of channel conditions between the base station and the UE.
The MCS could define a coding scheme for encoding the data, including adding redundancy bits to the underlying data as appropriate, to produce an encoded data set, and a modulation scheme that establishes how the bits of the encoded data set will then be physically modulated onto air-interface resource elements and ultimately how many bits each resource element will carry and thus how many bits in total each PRB could carry. LTE supports a range of MCSs ranging from low-order (with low encoding rate and with each resource element representing a low number of bits) to high-order (with high encoding rate and with each resource element representing a high number of bits). Further, LTE typically provides a mapping between channel conditions (e.g., UE-reported channel quality, per a channel quality indicator (CQI)) and applicable MCS.
Thus, when a base station is serving a UE and there is a quantity of data to be communicated downlink or uplink between the base station and the UE, the base station could determine the channel conditions between the base station and the UE (e.g., based on UE-reported channel quality) and could then select an appropriate MCS to use for the communication. Based on that MCS and the quantity of data to be communicated between the base station and the UE, the base station could then determine how many PRBs would be necessary to carry the data. And the base station could then allocate that number of PRBs for use to carry the data, allowing the communication to proceed accordingly.
This process could work for essentially any type of data to be communicated between the base station and the UE. By way of example, if the UE is engaged in a voice over Internet Protocol (VoIP) call, such as a voice over LTE (VoLTE) call, the UE could transmit and receive voice packets (carrying digitized voice data) periodically. For each such voice packet destined to the UE, the base station could determine the quantity of data defining the packet, the base station could determine an applicable MCS based on the UE's channel conditions, the base station could allocate a number of PRBs accordingly to carry the data, and the base station could transmit the data to the UE in the allocated PRBs. And likewise, for each such voice packet to be transmitted from the UE, the base station could determine the quantity of data defining the packet, the base station could determine an applicable MCS based on the UE's channel conditions, the base station could allocate a number of PRBs accordingly to carry the data, and the UE could transmit the data to the base station in the allocated PRBs.